In spiritualism and ghost stories, a mysterious substance that supposedly oozes from a medium's body during a séance; in biology, it's the outer layer of cytoplasm.
From Greek 'ektos' (outside) plus 'plasma' (molded substance, living substance). Coined in the 1880s for spiritualist phenomena, later borrowed by biologists for the outer cytoplasm layer.
Ectoplasm is the perfect word for explaining why 19th-century spiritualist mediums were always leaking glowing stuff during séances—it sounds scientific enough to fool audiences, even though it was essentially cotton gauze or phosphorescent paint.
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